VSEPR: Determining the Shapes of Molecules

1. Summarize in your own words the rules for writing Lewis electron-dot structures. Use and example of a simple molecule (not SO2, CO2, or H2O) to illustrate the application of these rules. NO3- . .

2. For the molecule you used in example in Question1 above, explain the reasoning in how the VSEPR theory would be used to deduce the geometric shape of this molecule.

Procedure:
For each molecule in the table below, list the number of total valence electrons in the molecule, draw the Lewis structure, indicate the molecular geometric shape and the approximate bond angles in the molecule. Look each shape up on one of the following websites:
Molecule Valence Electrons Lewis Structure Geometric Shape Approximate Bond Angles Sketch

Note: molecules C2H6 and C2H4 have 2 central atoms (carbons are bonded to each other). Look at the geometric shape on a single carbon.

Questions:
1. In the last 2 molecules you were asked to examine, there were multiple bonds present. How does the presence of a multiple bond (double or triple bond) affect your determination of the geometry of the molecule? Use C2H4 or CH2O to illustrate your discussion.
2. Although models cannot show this simply, for molecules like NF3 (whose structure you drew earlier), the actual bond angles may not exactly equal the angles predicted by VSEPR theory. For example, the F-N-F bond angles in NF3 are less than the 109.5° tetrahedral angle. Why do you think this might be so?

This question has the following supporting file(s):

Bonding Lab.rtf

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Solution Summary

The method of prediciton geometric shape of molecules is detailed and many examples are shown.

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Bonding Lab.rtf

1. Summarize in your own words the rules for writing Lewis electron-dot structures. Use and
example of a simple molecule (not SO2, CO2, or H2O) to illustrate the application of these
rules. NO3- ..
: O : Is that only valence electrons are included in the lewis structure.
|
N
// \
:O: :O:
``
2. For the molecule you used in example in Question1 above, explain the reasoning in how
the VSEPR theory would be used to deduce the geometric shape of this molecule.

Procedure:
For each molecule in the table below, list the number of total valence electrons in the molecule,
draw the Lewis structure, indicate the molecular geometric shape and the approximate bond
angles in the molecule. Look each shape up on one of the following websites:
Molecule Valence Electrons Lewis Structure Geometric Shape
Approximate Bond Angles Sketch
.. :F: .. | .. : F - C -- F : `` | ``
CF4 4+4(7)=32
:F: `` Tetrahedral

NH3 5+3(1)=8 .. H - N - H | H Trigonal Pyramid

SO42- 6+4(6)+2=32 __ __2- | .. ||
:O: || .. | .. | | : O - S - O : | | `` | `` || :O: | |__ ``
__| Tetrahedral
NH4+ 5+4(1)-1=8 _ _| | +| H | | | |
| H-N-H | | | || H | |_ _| Tetrahedral

H2 S 2(1)+6=8 .. H - S - H `` Linear

PO43-

HCl 1+7=8

NF3 5+3(7)=26 .. N /|\ :F: :F: :F: `` `` ``
Tetrahedral Trigonal pyramid

C2H4 see note 2(4)+4(1)=12 H H \ / C====C
/ \ H H

CH2O

Note: molecules C2H6 and C2H4 have 2 central atoms (carbons are bonded to each other). Look
at the geometric shape on a single carbon.

Questions:
1. In the last 2 molecules you were asked to examine, there were multiple bonds present.
How does the presence of a multiple bond (double or triple bond) affect your
determination of the geometry of the molecule? Use C2H4 or CH2O to illustrate your
discussion.
2. Although models cannot show this simply, for molecules like NF3 (whose structure you
drew earlier), the actual bond angles may not exactly equal the angles predicted by
VSEPR theory. For example, the F-N-F bond angles in NF3 are less than the 109.5°
tetrahedral angle. Why do you think this might be so?